Schwingungsspektroskopische Untersuchung der Aggregation und Isomerisierung von Modellpeptiden in der Jet-Expansion am Beispiel kleiner sekundärer Amide

Vibrational Spectroscopy of the aggregation and isomerization of model peptides in jet expansion using the example of secondary amides

by Thomas Forsting
Doctoral thesis
Date of Examination:2020-08-12
Date of issue:2021-08-06
Advisor:Prof. Dr. Martin A. Suhm
Referee:Prof. Dr. Martin A. Suhm
Referee:Prof. Dr. Burkhard Geil
Persistent Address: http://dx.doi.org/10.53846/goediss-8766

 

 

Files in this item

Name:DISS_Forsting_PUBLISHED_eDiss.pdf
Size:22.7Mb
Format:PDF

The following license files are associated with this item:

Abstract

English

Small secondary amides serve as simple and yet realistic model systems for hydrogen bonds in peptides and the rotational isomerization about the actual peptide bond. The preferred structures of small amide clusters (e. g. dimers and trimers) may represent benchmark systems for an accurate quantum chemical description of protein interactions. In this thesis, I examined the cis-/trans-isomerism and the cluster formation of N‑methyl­formamide, N-methylacetamide and formanilide (among others) with a combination of linear Raman and infrared supersonic jet techniques as well as with quantum chemical DFT-methods using the B3LYP functional with harmonic frequency calculations and vibrational perturbation theory. The Raman spectra were obtained with the custom-built and well established curry-jet setup which was successfully enhanced with a heatable feeding system to allow for measurements of less volatile substances e. g. formanilide or imidazole. As the major result of this thesis, it was shown for the first time that the most stable trimers of N-methylformamide and N-methylacetamide have a cyclic, barrel-like structure. This was proven spectroscopically by comparison of Raman and infrared jet spectra at different substance concentrations. This is in full agreement with theoretical DFT predictions as long as dispersion correction is used, which should thus be from now on the standard in DFT-calculations where intermolecular interactions play a significant role.
Keywords: jet expansion; vibrational spectroscopy; DFT calculations; peptide bond; secondary amides; dispersion correction; model peptide; N-methylacetamide; N-methylformamide; vibrational perturbation theory; harmonic frequency calculation; cis-/trans-isomerization; intermolecular interactions; Raman spectroscopy
 
Statistik